The invention relates to a circuit arrangement for monitoring two operating voltages of different polarity.
Such a circuit arrangement is especially necessary in devices used in information and data technology if an operating voltage deviates from its target value, so as to avoid, for example, erroneous data being output above a certain tolerance limit without this being recognized in time. For this purpose, the failure or the disturbance of an operating voltage is certainly to be indicated or the device switched off automatically.
In DE-C 25 26 346 is disclosed a circuit arrangement for monitoring the failure of one of various operating voltages necessary for operating electronic devices which voltages have different polarities. The circuit arrangement comprises a common reference line and a monitoring relay which is inserted in the power loop of one of the voltages to be monitored, which relay, when one of the voltages to be monitored fails, drops out and triggers an alarm. The relay is connected in series with a switching transistor whose base is connected to a zener diode. If the voltage on the anode of the zener diode drops below 0 volts, the switching transistor will be blocked and the relay will drop out.